1. Field of the Invention
The present invention relates to an adaptive wireless parameter control method, a QoS control device and a wireless communication system, and more particularly to an adaptive wireless parameter control method, a QoS control device and a wireless communication system, which fix wireless parameters adaptably, depending on quality of service required for packets to be transmitted, in transmitting the packets wirelessly.
2. Descriptions of the Related Arts
In next generation mobile communication systems (International Mobile Telecommunication-2000: IMT-2000), requirements for the maximum information transmission speed in accordance with “mobile environment”, “walking environment” and “quasi-stationary environment” are 144 kbps, 384 kbps and 2 Mbps, respectively, and genuine multimedia mobile communication can be realized in addition to voice service. However, when considering rapid spread of Internet, diversification and high capacity of information in recent years as well as progress of next generation Internet, development of a wireless access scheme for realizing an information transmission speed exceeding 2 Mbps in mobile communication is urgent.
Under such background, a scheme for realizing a high-speed packet transmission with the maximum information transmission speed of 2.4 Mbps based on IS-95 wireless interface is proposed in the literature (CDMA/HDR: A Bandwidth-Efficient High-Speed Wireless Data Services for Nomadic Users (P. bender, P. Black, M. Grob, R. Padovani, N. Sindhushayana, and A. Viterbi: IEEE Communication Magazine vol. 38, no. 7, pp 70-77, July 2000)). Furthermore, also in 3GPP (3rd Generation Partnership Project), the investigation for realizing a high-speed packet transmission with the maximum information transmission speed of about 8.5 Mbps, which expands W-CDMA wireless interface, has been performed.
In the high-speed packet transmission as described above, have been investigated applications of technologies including adaptive modulation/demodulation and error correction (channel encoding) based on an adaptive wireless link control (link adaptation) proposed in the literature (Symbol Rate and Modulation Level-Controlled Adaptive Modulation/TDMA/TDD System for High-Bit-Rate Wireless Data Transmission (T. Ue, S. Sampei, and N. Morinaga: IEEE Transaction. VT, pp 1134-1147, vol. 47, no. 4, November 1998)) and an automatic repeat request (ARQ) proposed in the literature (Automatic-Repeat-Request Error Control Schemes (S. Lin, D. Costello, Jr., and M. Miller: IEEE Communication Magazine, vol. 12, no. 12, pp 5-17, December 1984)).
The adaptive modulation/demodulation and error correction based on the link adaptation means a scheme for switching a data modulation multi-value, a spreading factor (SF), the number of multi-codes, and an encoding factor of the error correction to others depending on propagation environments for users, in order to effectively perform a high-speed data transmission. Herein, for example, as to the data modulation, the maximum throughput of the system can be increased by sequentially switching from the QPSK modulation, which is adopted in the present W-CDMA, to more efficient multi-value modulations, that is, 8 PSK, 16 QAM and 64 QAM, according to improvement of the propagation environments. To be concrete, when assuming that SF be equal to 4, the number of multi-codes be equal to 3 and a forward error correction factor be equal to ½, it is possible to perform ultra high-speed data transmission of 8.5 Mbps by use of W-CDMA wireless interface showing a chip rate of 3.84 Mcps when 64 QAM is used as a data modulation scheme.
Incidentally, in such broadband wireless access, diversification in requirements for quality of service (QoS) such as a transmission speed, a transmission delay and a residual BER (Bit Error Ratio) is predicted.
For example, in traffic such as voice and video for which real time transmission is required, increases in a transmission delay and in delay fluctuation cause significant deterioration of quality. Accordingly, bit error concerning the packets is permitted within a range satisfying communication quality without dumping of the packet that includes the error so that a transmission delay time from a transmission end to a receiving end must be constrained to a range of the requirements in accordance with the quality of services (QoS).
On the other hand, in non-real time traffic such as file transfer and WWW (World Wide Web) browsing, though a demand for the transmission delay is weaker compared to the real time traffic, transmission with high throughput and reliability, which is basically free from error, is required.
Although an automatic repeat request (ARQ) in the packet transmission scheme is an effective technology for high reliability transmission, it causes transmission delay and delay fluctuation in the real time traffic.
Furthermore, while receiving quality is improved by performing channel encoding with high error correction capability, throughput is decreased due to a decrease in frame efficiency.
Accordingly, in order to provide multimedia services effectively in such a packet transmission scheme including a mix of various types of traffic, effective applications of an error control (QoS control) technology between wireless sections are more important. Specifically, when the error control (QoS control) by a technology such as an error protection using an automatic repeat request between a wireless sections and a forward error correction (FEC) is performed, different standards for respective kinds of traffics must be applied.
However, in conventional link adaptation technology, wireless parameters including the optimum modulation scheme and the forward error correction method which are adapted only to a wireless link state (conditions of propagation path) have been merely selected, and QoS based on requests concerning traffic characteristics, in particular delay, has not been considered.
From the above described viewpoints, it has been proved to be very useful to select wireless parameters including the modulation scheme, the forward error correction scheme, and the upper limit of repeat times of the automatic repeat request while taking into consideration the trade off between advantages and disadvantages in the error modulation scheme adaptively switched in response to the QoS requirements. Moreover, it is inferred that combinations of respective adoptive selections vary in accordance with the QoS requirements.